Electric metal-working apparatus



E. THOMSON.

ELECTRIC METAL WORKING APPARATUS. APPLICATION m AUG- 28, 191s.

Patented Mar. 23, 1920.

INVENTOR A TTORNEYS Electric Metal-Working Apparatus,

UNITED STATES PATENT OFFICE.

ELIHU THOMSON, OF SITAIHIPSCOTJI, MASSACHUSETTS, ASSIGNOR T0 THOMSON ELECTRIC WELDING COMPANY, OF LYNN, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS.

ELECTRIC METAL-WORKING- APPARATUS.

Specification of Letters Patent. Patented Mar. 23, 1920.

Application filed August 28, 1918. Serial No. 251,758.

To all whom it may concern:

Be it known that I, Ennzm THOMSON, a citizen of the United States, and a resident of Swam scott, in the county of Essex and State of assachusetts, have invented certain new and useful Improvements in which the following is a specification.

My invention relates to that class of electrical metal working apparatus in which heavy alternating or other rapidly varying electric currents are employed and inwhioh, owing to the disposition of the leads conveying the current to and from the work or workholders, there is a free space between said leads which may becomefthe locus of an intense magnetic field caus' by self-induction, a voltage drop in sai leads.

My invention is particularly useful for apparatus in which an alternating current transformer supplies the heavy electric current to the clamps or holders though flexible leads permitting free movement of the workholders.

When the leads. from the alternating cur-' rent transformer .for electric welding or similar uses are carried away from the transformer so as to leave a free s ace between such leads, there is a voltage rop depending upon the extent of this s ace and the. length of the leads. This vo tage drop is not wholl due to resistance but may be in fact largely inductive owing to the formation of a field between the connections to the work holder or work in which the mag netic density may rise to a high point. This would be largely obviated if the leads or conductors from the transformer ran nearly parallel and close together, but on account of the motion of the electrodes and other contingencies it is not always possible to so arrange them. The clam s or holders especially for electric welding, must have a play toward and from each other and 1t 1s also desirable to make as direct connections as possible to said holders from the active part of the welding transformer itself.

My present invention consists m means for' overcoming the voltage drop due to the formation of such magnetic fie d and consists essentially in surrounding the locus of the field with a counter inductive circuit or shield so as to annul the contrary induction due to the production of the magnetic offects. This shield may be applied between the conductors and the locus of the field or may be applied at one or both sides of said conductors and in such manner as to in effect still surround or inclose said field.

In carrying out my invention the inductive circuit or shield would be preferably formed of copper and might take the form of a copper band and, when applied between the leads and the locus of the field, may' Referring to Fig. 1, T indicates any form r of alternating current transformer for welding or similar work with its iron core, massive secondary and primary coil related to the secondary as usual in this class of devices. F F indicates the flexible leads formed of bundles or laminae of conducting material extending from the terminals of the massive secondary to the workholders or electrodes C G, which may be some distance from the transformer.

In the present illustration of my invention said leads are shown as flexible to permit movement of the electrodes or workholders to and from one another, but, as will be readily understood, the flexibilit might be absent and other means provi ed for,permitting a movement of the workholders or clamps, as well. understood in the art.

K With the transformer leads thus disposed there is a space between them which, during heavy work, becomes the locus of an intense magnetic fieldand causes an inductive drop seat of an indu propose to apply a shield G of good conducting material, referably a copper band closed on itself and practically surrounding said field. In the form of my invention shown in Fig. 1, it may outline and nearly fill the space between the flexible leads, as

shown. Said shield may be a hollow figure or closed electric circuit and its extent or depth may coincide with the depth of the leads F F or may be greater or less than that depth. The shield may even be developed with turned-out edges to partly inclose the leads F F all that is necessary being that they shall have a sufiicient amount of copper or good conducting material to inclose the space A fairly well. On the tendency to produce a powerful field in A by the welding currents at F F, which at any moment are in opposite direction, induced currents are developed in the shield, which oppose the magnetism of the space A and reduce it to a low value. The shield might be made to conform closely to the leads and be made flexible so that it would move or collapse more or less with the motion toward each other of the welding clamps; but this thoroughness of arrangement will he rarely necessary for annulling the major part of the effect.

Further modification and arrangements may of course be made, as for instance the shield may be a closed coil or wire wound up sultably or may be several closed circuits superposed, or in any way related to each other, provided' they surround the spacewhich is magnetized by the heavy alternating currents and are adapted to form the current.

It will be evident that instead of a single shield or a closed circuit G applied as shown in Fig. 1, I may employ a flat shield G located directly in front of the conductors F F, when flexible, and having about the same figure s the shield G, but larger in breadth and I may add, for more perfect results, a

similar one back of the conductors F F.

This is shown in Figs. 3 and 4. Such a p'air of shields in no wise interferes with the clamps C C or conductors F F, and if arranged close to F F, front and back, are al most as efl'ective as the shield in the position Fig. 1. It will be seen that this shield does not occupy the space between the leads, but

nevertheless. surrounds the magnetic fieldand largely neutralizes it.

What I claim as my invention is:

1. In an electric metal working apparatus,

provided with heavy current leads separated from one another by a free air space and connected to workholders movable to and from one another, of a counter inductive circuit or shield surrounding said space and adapted to allow free movement of said workholders.

' 3. In an electric metal working apparatus, the combination with a transformer having leads connected directly to movable workholders and separated from one another by an air space, of a shield of good conducting material surrounding said air space.

4:. In an electric metal working apparatus, the combination with a transformer having flexible leads connected directly to movable workholders and separated from one another by an air space, of a shield of good conducting material surroun said air space but separated from the 1 to allow freedom of movement thereof.

. Signed at Lynn, in the county of Essex and State of Massachusetts, this 3d day of August, A. D. 1918'.

ELIHU THOMSON. Witnesses:

F. B. Townsmm, FRANK Boner-en. 

